Prism, imaging device and lighting device including the same, and prism manufacturing method

ABSTRACT

A prism  30  includes a prism body  30 . The prism body  31  is formed into a polygonal column. At least one of a plurality of ridges  35, 36  of the prism body  31  is formed into an R-plane.

RELATED APPLICATIONS

This application is the U.S. National Phase under 35 U.S.C. §371 ofInternational Application No. PCT/JP2006/322258, filed on Nov. 8, 2006,which in turn claims the benefit of Japanese Application No.2005-334214, filed on Nov. 18, 2005, the disclosures of whichApplications are incorporated by reference herein.

TECHNICAL FIELD

In recent years, prisms are widely used as essential parts of variouskinds of optical equipment, such as DSCs (digital still cameras), DVCs(digital video cameras), cameras for mobile phones, projectiontelevisions, and the like, and the range of uses thereof is expanding.While, demands for higher precision, compaction, and weight reduction ofthe various optical equipment are increasing. In association therewith,the prisms used in the various optical equipment are required to havehigher performance, such as higher precision, higher functionality,higher strength, and the like.

A general triangular prism includes three side faces as optical functionplanes and two end faces as non-optical function planes. As a glass-madeprism manufacturing method, a generally-called press molding method isknown in which a material to be molded is heated and pressed and then iscooled (see, for example, Patent Document 1).

When a prism is molded by the press molding method disclosed in PatentDocument 1, each ridge where the planes are intersected with one anotheris formed sharply. Accordingly, in handling the prism, specifically, inconveyance, in mounting to optical equipment, and the like, the ridgesmay be broken or chipped by external impact. For this reason, desiredprism performance cannot be obtained, and the yield of the opticalequipment lowers.

For tackling the above problems, namely, for suppressing breakage andchipping of the ridges, a prism of which ridges are chamfered afterpress molding has been proposed (see, for example, Patent Document 2):

Patent Document 1: Japanese Patent Application Laid Open Publication No.7-69651A

Patent Document 2: Japanese Patent Application Laid Open Publication No.6-103101A

SUMMARY OF THE INVENTION Problems that the Invention is to Solve

In Patent Document 2, however, a post treatment is added after prismmolding, increasing the number of processing steps and costs. Further,the ridges of the prism before the post treatment are sharp yet, stillremaining the problems of breakage and chipping.

The present invention has been made in view of the foregoing and has itsobject of providing a prism of which breakage and chipping hardly occur.

Means for Solving the Problems

A prism according to the present invention includes: a prism body formedinto a polygonal column. At least one of a plurality of ridges of theprism body is formed into an R-plane.

An imaging device according to the present invention includes: a lightreceiving element; and a prism. The prism includes a prism body formedinto a polygonal column. At least one of a plurality of ridges of theprism body is formed into an R-plane. The prism body is in a form of aright triangular prism including two orthogonal side faces which areintersected at a right angle with each other and an inclined side facewhich is inclined with respect to the two orthogonal side faces. Theprism body is arranged so that incident light to the prism body isreflected by the inclined side face toward the light receiving element.

A lighting device according to the present invention includes: a lightsource; and a prism. The prism includes a prism body formed into apolygonal column. At least one of a plurality of ridges of the prismbody is formed into an R-plane. The prism body is in a form of a righttriangular prism including two orthogonal side faces which areintersected at a right angle with each other and an inclined side facewhich is inclined with respect to the two orthogonal side faces. Theprism body is arranged so that light from the light source is reflectedby the inclined side face.

In a first prism manufacturing method according to the presentinvention, a spherical base material is press-molded while being heated.A prism body formed into a polygonal column is formed. At least one of aplurality of ridges of the prism body is formed into an R-plane.

In a second prism manufacturing method according to the presentinvention, a base material in a column shape, each end face of which isprojected in a convex form, is press-molded while being heated. A prismbody formed into a polygonal column is formed. At least one of aplurality of ridges of the prism body is formed into an R-plane.

Effects of the Invention

The present invention can provide a prism of which breakage and chippinghardly occur.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram showing a configuration of a main part of an imagingdevice according to Embodiment 1 of the present invention.

FIG. 2 is a perspective view of a prism according to Embodiment 1.

FIG. 3 is a sectional view showing a construction of a manufacturingapparatus for press-molding a prism.

FIG. 4 shows a base material formed in a column shape of which each endface is projected in a convex form, wherein FIG. 4( a) is a front viewand FIG. 4( b) is a side view.

FIG. 5 is a side view of a spherical base material.

FIG. 6 is a diagram showing a configuration of a main part of a lightingdevice according to Embodiment 2 of the present invention.

EXPLANATION OF THE REFERENCE NUMERALS

-   -   1 imaging device    -   2 lighting device    -   11 light receiving element    -   30 prism    -   31 prism body    -   32 side face    -   32 a light incident plane (orthogonal side face)    -   32 b light exit plane (orthogonal side face)    -   32 c light reflection plane (inclined side face)    -   33 a, 33 b end face    -   35, 36 ridge    -   42 upper die    -   43 lower die    -   44 mold body    -   48 inner space    -   50 base material    -   51 light source

BEST MODE FOR CARRYING OUT THE INVENTION

Embodiments of the present invention will be described below withreference to the accompanying drawings.

Embodiment 1

FIG. 1 shows an imaging device 1 according to Embodiment 1 of thepresent invention. The imaging device 1 includes a light receivingelement 11, a plurality of lens groups (specifically, a first lens group12, a second lens group 13, and a third lens group 14), and a prism 30.

The first lens group 12 is arranged so as to be exposed from the imagingdevice 1 for receiving external light. The external light made incidentfrom the first lens group 12 is made incident to the prism 30. Theincident light is converted by the prism 30 to light different indirection of the optical axis. The converted light is imaged on thelight receiving element 11 through the second lens group 13 and thethird lens group 14. The imaged image is converted to an electric signalin the light receiving element 11 and is output to be recorded in arecoding section (not shown), such as a memory or the like. The lightreceiving element 11 may be composed of, for example, a charge coupleddevice (CCD), a complementary metal oxide semiconductor (CMOS), or thelike.

The prism 30 includes a prism body 31 formed into a polygonal column(including a truncated pyramid). At least one of a plurality of ridges35, 36 of the prism body 31 is formed into an R-plane. Accordingly, theridge 35 or 36 formed into the R-plane is prevented from being brokenand chipped.

The prism body 31 in a polygonal column includes a plurality of sidefaces 32 serving as optical function planes and end faces 33 a, 33 bserving as non-function planes. Each optical function planes herein is aplane having an optical function that transmits and reflects necessarylight for actual use thereof while the non-optical function planes is aplane having no optical function. The ridges 35 formed between the sidefaces 32 and the adjacent end faces 33 a, 33 b are formed into R-planes.Further, the ridges 36 formed between the side faces 32 adjacent to eachother are formed into R-planes. Hence, the ridges 35, 36 formed into theR-planes are prevented from being broken and chipped.

In order to secure high optical performance by suppressing breakage andchipping of the prism 30, preferably, all of the plurality of ridges 35,36 of the prism body 31 are formed into the R-planes.

For example, as shown in FIG. 2, the prism body 31 may be formed into aright triangular prism including orthogonal side faces which areintersected at a right angle with each other and an inclined side facewhich is inclined with respect to the orthogonal side faces. In theprism body 31, the orthogonal side faces serve as a light incident plane32 a and a light exit plane 32 b, and the inclined side face serves as alight reflection plane 32 c. The prism 30 is so formed that light madeincident perpendicularly from the light incident plane 32 a is reflectedby the light reflection plane 32 c and exits from the light exit plane32 b. In the imaging device 1, the prism 30 is so arranged that thelight incident plane 32 a is located on the first lens group 12 sidewhile the light exit plane 32 b is located on the second lens group 13side.

In the prism body 31, ridges 35 a, 35 b, 35 c respectively formedbetween the first end face 33 a and the light incident plane 32 a, thelight exit plane 32 b, or the light reflection plane 32 c, which areadjacent to the first end face 33 a, are formed into the R-planes. Inthe prism body 31, ridges 35 d, 35 e, 35 f respectively formed betweenthe second end face 33 b and the light incident plane 32 a, the lightexit plane 32 b, or the light reflection plane 32 c, which are adjacentto the second end face 33 b, are formed into the R-planes. Accordingly,the ridges 35 a to 35 f formed into the R-planes are prevented frombeing broken and chipped.

Further, in the prism body 31, ridges 36 a, 36 b, 36 c respectivelyformed between the light incident plane 32 a and the adjacent light exitplane 32 b, between the light exit plane 32 b and the adjacent lightreflection plane 32 c, and between the light reflection plane 32 c andthe adjacent light incident plane 32 a are formed into the R-planes.Accordingly, the ridges 35, 36 are prevented from being broken andchipped by external impact in conveyance, in mounting to opticalequipment, and the like, with a result that the yield of the prism 30 isprevented from lowering and a high-quality prism can be provided.

The material of the prism 30 is not limited especially and may beplastic or glass including cyrstallized glass, for example. A glassmaterial is especially preferable. When the prism 30 is made of glass,high accuracy of form, high thermal resistance, high mechanicaldurability, and high homogeneity can be achieved. In addition, sinceglass is comparatively small in thermal expansion coefficient andphotoelastic constant, the prism 30 is hardly deformed even if theimaging device 1 is increased in temperature, causing less or nodegradation of the optical characteristics of the prism 30.

Moreover, the refractive index of the glass-made prism 30 can beincreased comparatively easily. The prism 30 having a high refractiveindex shortens the length of the optical path of an optical system (thelens groups 12 to 14, the prism 30, and the light receiving element 11)of the imaging device 1. Thus, the imaging device 10 can be compacted.

Increased refractive index of the prism 30 increases the lightreflectance of the light reflection plane 32 c. The light reflectionplane 32 c is preferable to having 90% or greater light reflectance withrespect to visible light (light having a wavelength in the range between300 nm and 700 nm, both inclusive) made incident perpendicularly to theprism body 31 from the light incident plane 32 a. More preferably, thelight reflectance thereof is 95% or greater. For achieving such a highreflectance, the refractive index with respect to the D line (lighthaving a wavelength of 589 nm) of the prism 30 is preferably 1.6 orgreater. More preferably, the refractive index thereof is 1.65 orgreater. Preferably, the prism 30 has a high transmittance with respectto visible light.

For example, in the case where the prism 30 has a low refractive index(for example, where the prism 30 is made of grass having a lowrefractive index or plastic), a light reflection film (not shown) may beformed on the light reflection plane 32 c. With the light reflectionfilm formed, the reflectance of the light reflection plane 32 cincreases. This achieves high light utilization efficiency. The lightreflection film may be made of gold, aluminum, or the like, for example.

FIG. 3 shows a partial sectional view of a manufacturing apparatus 40 ofthe prism 30. The manufacturing apparatus 40 includes molding dies 41for press-molding the prism 30. The molding dies 41 include: a pair ofan upper die 42 and a lower die 43; and a mold body 44 to which theupper die 42 and the lower die 43 are inserted slidably. The moldingfaces of the dies, namely, faces forming an internal space 48 to which abase material 50 is inserted are processed into forms having a desiredaccuracy for molding the optical function planes of the prism 30. Forproviding high strength to the upper die 42, the lower die 43, and themold body 44, they are preferably made of hard metal. Alternatively,stainless steel (for example, STAVAX, a product by Uddeholm KK) may beused as the material of the upper die 42, the lower die 43, and the moldbody 44. Optionally, a protection film may be formed on the moldingfaces of the molding dies 41 for enhancing the mold releasecharacteristic of the prism 30 and for suppressing oxidation andcorrosion of the molding dies 41. For example, the molding faces may besubjected to electroless nickel plating.

A press head 45 changeable in temperature is mounted at the top of theupper die 42 for vertically moving the upper die 42. The press head 45includes pressing means 46. A press stage 47 changeable in temperatureis mounted at the bottom of the lower die 43.

Description will be given to a method for manufacturing the prism 30with the use of the above manufacturing apparatus 40.

First, the base material 50 is inserted into the internal space 48defined and formed by the upper die 42 and the lower die 43 in the moldbody 44 of the molding dies 41. The base material 50 is made of glass(K-VC78, a product by Sumita Optical Glass, Inc. or the like), forexample. The base material 50 is formed into a column shape of whicheach end face is projected in a convex shape, as shown in FIG. 4. Thebase material 50 is inserted so that the column-shaped base material 50is held at the side face thereof between the upper die 42 and the lowerdie 43. The base material 50 may be formed into a spherical shape, asshown in FIG. 5.

Subsequently, the upper die 42 and the lower die 43 are heated by thepress head 45 and the press stage 47. The heated upper die 42 and theheated lower die 43 heat the base material 50 to a predeterminedtemperature. For example, the base material 50 is heated up to aroundthe deformation point thereof (around 570° C., for example).

Next, the cylinder 46 is driven to lower the press head 45 to press-moldthe base material 50. Press molding is performed in such a manner thatthe relative positional relationship between the upper die 42 and thelower die 43 is changed to a range satisfying a condition that thevolume of the base material 50 is smaller than the volume of the innerspace 48 of the molding dies 41 at the time when the press molding iscompleted.

The heating, is stopped with the relative positional relationshipbetween the upper die 42 and the lower die 43 maintained. Then, the basematerial 50 is cooled to a temperature around Tg (glass transition pointthereof) by the press head 45 and the press stage 47.

Finally, the cylinder 46 is driven to raise the press head 45, and theupper die 42 is taken out from the mold body 44 to open the molding dies41. Then, the press-molded prism 30 is taken out.

The prism 30 manufactured by the above manufacturing method includes theridges 35, 36 formed into the R-planes. The ridges 35, 36 are formedinto the R-planes simultaneously with formation of the optical functionplanes and the non-optical function plane, so that brakeage and chippingcan be prevented without performing a post treatment, thereby preventingthe yield of the prism 30 from lowering.

The light incident plane 32 a and the light exit plane 32 b areintersected at a right angle with each other in Embodiment 1, but may beintersected at any angle.

Further, though the prism 30 in Embodiment 1 is so formed that lightmade incident from the light incident plane 32 a is reflected by thelight reflection plane 32 c and exits from the light exit plane 32 b,the prism 30 may be formed so that light from the first lens group 12 isreflected by an external face as the light reflection plane 32 c andexits on the second lens group 13 side. In other words, the prism 30 isused as a prism of external face reflection type.

Embodiment 2

While Embodiment 1 describes the imaging device 1 using the prism 30,the prism 30 may be used in any optical devices other than the imagingdevice 1. For example, it may be used in a lighting device. InEmbodiment 2, a lighting device 2 including the prism 30 will bedescried in detail with reference to FIG. 6. In the description ofEmbodiment 2, the same reference numerals are assigned to the sameconstitutional elements as those in FIG. 2 to FIG. 5 for omittingdetailed description thereof.

FIG. 6 shows the lighting device 2 according to Embodiment 2 of thepresent invention. The lighting device 2 according to Embodiment 2 ofthe present invention includes a light source 51, lens groups (a firstlens group 52, a second lens group 53, and a third lens group 54), andthe prism 30. In Embodiment 2, the prism 30 is so arranged that thelight incident plane 32 a of the prism body 31 is located on the lightsource 51 side while the light reflection plane 32 c thereof is locatedon the first lens group 52 side. The light source 51 is a light sourcethat emits parallel light or diffused light. The light emitted from thelight source 51 is transmitted through the first lens group 52 and thesecond lens group 53 and is made incident to the light incident plane 32a of the prism 30. The light made incident to the prism 30 is reflectedby the light reflection plane 32 c and exits from the light exit plane32 b. The light exited from the prism 30 is transmitted through thethird lens group 54 to be allowed to exit from the lighting device 2.

INDUSTRIAL UTILIZATION

As described above, the present invention is useful for a prism, animaging device and a lighting device each including it, a prismmanufacturing method, and the like.

1. A prism, comprising: a prism body formed into a polygonal column,wherein the prism body includes optical function planes and thenon-optical function planes, and ridges formed between the respectiveoptical function planes and the respective non-optical function planes,which are adjacent to each other, are formed into round shapes.
 2. Theprism of claim 1, wherein the prism body includes a plurality of sidefaces and two end faces which form the polygonal column and serve as theoptical function planes or the non-optical function planes.
 3. The prismof claim 1, wherein the prism body in the polygonal column includes aplurality of side faces serving as optical function planes and two endfaces serving as non-optical function planes, and ridges formed betweenadjacent optical function planes are formed into round shapes.
 4. Theprism of claim 1, wherein all of the plurality of ridges are formed intoround shapes.
 5. The prism of claim 1, wherein the prism body is in aform of a right triangular prism including two orthogonal side faceswhich are intersected at a right angle with each other and an inclinedside face which is inclined with respect to the two orthogonal sidefaces.
 6. The prism of claim 5, wherein the inclined side face isprovided with a reflection film.
 7. The prism of claim 5, wherein theprism body has a reflectance of 90% or greater at the inclined side facewith respect to visible light made incident from one of the twoorthogonal side faces perpendicularly to the one orthogonal side face.8. The prism of claim 1, wherein the prism body is made of glass.
 9. Theprism of claim 1 wherein the prism body has a refractive index of 1.65or greater with respect to a D line thereof.
 10. An imaging devicecomprising: a light receiving element; and a prism including a prismbody formed into a polygonal column, wherein: the prism body includesoptical function planes and the non-optical function planes, ridgesformed between the respective optical function planes and the respectivenon-optical function planes, which are adjacent to each other, areformed into round shapes, and the prism body is in a form of a righttriangular prism including two orthogonal side faces which areintersected at a right angle with each other and an inclined side facewhich is inclined with respect to the two orthogonal side faces and isarranged so that incident light to the prism body is reflected by theinclined side face toward the light receiving element.
 11. The imagingdevice of claim 10, wherein the prism body is arranged so that theincident light is made incident from one of the two orthogonal sidefaces and exits from the other orthogonal side face.
 12. A lightingdevice, comprising: a light source; and a prism including a prism bodyformed into a polygonal column, wherein: the prism body includes opticalfunction planes and the non-optical function planes, ridges formedbetween the respective optical function planes and the respectivenon-optical function planes, which are adjacent to each other, areformed into round shapes, and the prism body is in a form of a righttriangular prism including two orthogonal side faces which areintersected at a right angle with each other and an inclined side facewhich is inclined with respect to the two orthogonal side faces and isarranged so that light from the light source is reflected by theinclined side face.
 13. The lighting device of claim 12, wherein theprism is arranged so that light from the light source is made incidentfrom one of the two orthogonal side faces and exits from the otherorthogonal side face.
 14. A method for manufacturing a prism including aprism body formed into a polygonal column, the prism body includingoptical function planes and the non-optical function planes, ridgesformed between the respective optical function planes and the respectivenon-optical function planes, which are adjacent to each other, beingformed into round shapes, the method comprising the step of:press-molding while heating a spherical base material to obtain theprism.
 15. The prism manufacturing method of claim 14, wherein the pressmolding step is performed, with the use of a pair of an upper die and alower die and a mold body to which the upper die and the lower die areinserted slidably, in such a manner that the base material is insertedinto an inner space defined and formed between the upper die and thelower die in the mold body and a relative positional relationshipbetween the upper die and the lower die is changed to a range satisfyinga condition that a volume of the base material is smaller than a volumeof the inner space at a time when the press molding is completed.
 16. Amethod for manufacturing a prism including a prism body formed into apolygonal column, the prism body including optical function planes andthe non-optical function planes, ridges formed between the respectiveoptical function planes and the respective non-optical function planes,which are adjacent to each other, being formed into round shapes, themethod comprising the step of: press-molding while heating a basematerial in a column shape, each end face of which is projected in aconvex form, to obtain the prism.
 17. The prism manufacturing method ofclaim 16, wherein the press molding step is performed, with the use of apair of an upper die and a lower die and a mold body to which the upperdie and the lower die are inserted slidably, in such a manner that thebase material is inserted into an inner space defined and formed betweenthe upper die and the lower die in the mold body and a relativepositional relationship between the upper die and the lower die ischanged to a range satisfying a condition that a volume of the basematerial is smaller than a volume of the inner space at a time when thepress molding is completed.